Abstract:
Dothistroma septosporum is a haploid fungal pathogen that causes a serious needle
blight disease of pines, particularly as an invasive alien species on Pinus radiata
in the Southern Hemisphere. During the course of the last two decades,
the pathogen has also incited unexpected epidemics on native and non-native
pine hosts in the Northern Hemisphere. Although the biology and ecology of
the pathogen has been well documented, there is a distinct lack of knowledge
regarding its movement or genetic diversity in many of the countries where it
is found. In this study we determined the global population diversity and structure
of 458 isolates of D. septosporum from 14 countries on six continents using
microsatellite markers. Populations of the pathogen in the Northern Hemisphere,
where pines are native, displayed high genetic diversities and included
both mating types. Most of the populations from Europe showed evidence for
random mating, little population differentiation and gene flow between countries.
Populations in North America (USA) and Asia (Bhutan) were genetically
distinct but migration between these continents and Europe was evident. In the
Southern Hemisphere, the population structure and diversity of D. septosporum
reflected the anthropogenic history of the introduction and establishment of
plantation forestry, particularly with Pinus radiata. Three introductory lineages
in the Southern Hemisphere were observed. Countries in Africa, that have had
the longest history of pine introductions, displayed the greatest diversity in the
pathogen population, indicating multiple introductions. More recent introductions
have occurred separately in South America and Australasia where the
pathogen population is currently reproducing clonally due to the presence of
only one mating type.
